KevinRum

Thank You newdude! That makes sense and great information. I will forward this to the mechanic as I am still waiting for it to be repaired for the third time. They now say the part or on backorder because there is a shortage in the area ... go figure!

Sorry, misfires on cylinder 6 and 1, not five. They said the VLOM was tested and met specifications, but not replaced. Not sure if I mentioned the oil pressure sensor was replaced early in these issues. Is the pressure control solenoid different than the pressure sensor and where is it located? I doubt the pressure control solenoid was changed but considering I have very high pressure, it would seem the 2-stage pump is kicking in ... but beyond my knowledge base. Also, the tensioner was not part of the parts RR list so doubt that was replaced either. Thank you for your help and input!

Hello Everyone! I seem to have a compounding issue with my 2014 GMC Sierra SLT 5.3L which I have been the owner since 2016. It started about 7 weeks ago with an oil pump failure code appearing often although always had oil pressure, in fact it would fluctuate between 18psi at stop light to almost 80psi when accelerating very fast. Took 3 weeks to get into mechanic and drive it carefully during this time resetting the code each time it showed up (each leg to and from work, 28miles). After mechanic connected his master gauge, he said pressure was all over the place so recommended replacing the oil pump. Once replaced, no more error codes although my pressure still fluctuated between 18psi and now buries the needle way past 80+ psi when under high load. If the gauge went to 90 or so I felt like it would still bury it. Mechanic said high pressure better than low although in the 160K miles already driven, I have never seen it reach much over 70 psi even while pulling the camper … until the 2-stage oil pump error code. This is just the beginning folks. Not a week passed and started getting random misfire code. Since it was rainy when this occurred, we figured it was plugs or wires. Code went away on its own while on my way to the parts store (rain cleared up and now sunny), purchased and changed them anyway. No problems for few days till it snowed Easter evening. The next morning while leaving for work, misfire cylinder 5, so I turned around and quickly installed the new coil pack. This did not fix issue. Drove to work with misfire then had it towed to the mechanic so I wouldn’t complicate the issue. Problem was a collapsed lifter, intake side. Mechanic replaced all lifters. Drove less than 100 miles and misfire cylinder 5 again! Immediately towed back to the mechanic who verified exhaust lifter (new) failure. In fact, mechanic said it was destroyed. Mechanic replaced that lifter under GM parts warrantee and in less than another 100 miles, misfire cylinder 1. Just before this latest lifter failure (so I assume) I read an old code P0451. Q: Could the P0451 have anything to do with my lifter rash and what the heck is the mechanic missing about all these failures? I really think the large change in oil pressure, even before the new pump, is key to what might be causing the lifter failures, but the mechanic keeps dismissing it. Can anyone help me understand?